Differentiation of the species

The genus Allochromatium contains two easily distinguished groups of species. A. vinosum and A. minutissimum are physiologically versatile species that do not require growth factors, grow chemoautotrophically, have rather high tolerance towards sulfide, and use thiosulfate, hydrogen, and organic compounds as photosynthetic electron donors. A. warmingii, on the other hand, is a specialized species that requires vitamin B12 as a growth factor,

The strain HPC, which was tentatively identified as a strain of "Chromatium vinosum" (Bauld et al., 1987), was certainly mis-identified and does not belong to this species. This strain has an optimum salt concentration for growth of 2.5-4.5% NaCl, which may indicate membership to the genus Halochromatium. Further studies should allow its taxonomic position to be determined.

Further Reading

Imhoff, J.F., Silling, J. and Petri, R. 1998. Phylogenetic relationships among the Chromatiaceae, their taxonomic reclassification and description of the new genera Allochromatium, Halochromatium, Isochro-matium, Marichromatium, Thiococcus, Thiohalocapsa, and Thermochro-matium. Int. J. Syst. Bacteriol. 48: 1129-1143.

of the genus Allochromatium tolerates only rather low concentrations of sulfide, and is a strictly anaerobic and phototrophic bacterium. Differential characteristics of Allochromatium species are shown in Table BXII.y.4 of the chapter describing the family Chromatiaceae. Presently known Al-lochromatium species can easily be distinguished on the basis of their cell diameter: Cells 2.0 |im wide, A. vinosum; cells 1-1.2 |im wide, A. minutissimum; cells 3.5-4.0 |m wide, A. warmingii.

List of species of the genus Allochromatium

1. Allochromatium vinosum (Ehrenberg 1838) Imhoff, Suling and Petri 1998b, 1141VP (Chromatium vinosum (Ehrenberg 1838) Winogradsky 1888, 99; Monas vinosa Ehrenberg 1838,11.)

Cells are rod shaped, 2 X 2.5-6 |m, occasionally longer. Globules of S0 evenly distributed within the cell (Fig. BXII.y.6). Single cells are colorless, color of growing cultures first yellowish to orange-brown, later brownish red. Photosynthetic pigments are bacteriochlorophyll a and ca-rotenoids of the normal spirilloxanthin group.

Grow phototrophically under anoxic conditions in the light or chemotrophically under microoxic to semioxic conditions in the dark (Kampf and Pfennig, 1980). Both chem-otrophic and phototrophic growth is possible under auto-trophic and heterotrophic conditions. Photosynthetic electron donors: sulfide, sulfur, thiosulfate, sulfite, molecular

FIGURE BXII.y.6. Allochromatium vinosum ATCC 17899 cultured pho-toautotrophically with sulfide. The cells contain sulfur globules. Bright-field micrograph. Bar = 5 |m.

hydrogen, formate, acetate, propionate, pyruvate, fumarate, malate, and succinate. Some strains utilize butyrate. Not utilized: sugars, sugar alcohols, alcohols, benzoate, citrate, and amino acids. Assimilatory sulfate reduction occurs (Thiele, 1968). Nitrogen sources: ammonium salts and N2.

Mesophilic freshwater bacterium with optimum growth at 25-35°C and pH 7.0-7.3 (range 6.5-7.6). Marine isolates may tolerate or require low concentrations of NaCl.

Habitat: ponds and lakes with stagnant freshwater, sewage lagoons, brackish waters, estuaries, salt marshes, and marine habitats containing hydrogen sulfide and exposed to light. Among the most widely occurring species of the family Chromatiaceae.

The mol% G + C of the DNA is: 61.3-66.3 (Bd); type strain 64.3 (Bd).

Type strain: D, BN 5110, ATCC 17899, DSM 180.

GenBank accession number (16S rRNA): M26629.

2. Allochromatium minutissimum (Winogradsky 1888) Imhoff, Suling and Petri 1998b, 1141VP (Chromatium minutissimum Winogradsky 1888, 100.)

mi.nu.tis'si.mum. L. neut. sup. adj. minutissimum very small, smallest.

Cells are rod shaped, 1-1.2 X 2 |im. Other characteristics are the same as for A. vinosum.

Type strain: MSV, BN 5310, DSM 1376.

GenBank accession number (16S rRNA): Y12369.

3. Allochromatium warmingii (Cohn 1875) Imhoff, Stiling and Petri 1998b, 1141VP (Chromatium warmingii (Cohn 1875) Migula 1900, 1048; Monas warmingii Cohn 1875, 167.) war.min'gi.i. M.L. gen. n. warmingii of Warming; named for E. Warming, a Danish botanist.

Cells ovoid to rod shaped, 3.5-4.0 X 5-11 |m, sometimes longer, motile by a flagellar tuft which is usually 1.52 times the cell length and visible by brightfield or phase-contrast microscopy. In the presence of sulfide and light, globules of S0 are predominantly located at the two poles of the cell. Dividing cells form additional sulfur globules near the central division plane (Fig. BXII.y.7). Color of individual cells is grayish to slightly pink, color of cell suspensions pinkish to purple-violet. Photosynthetic pigments are bacteriochlorophyll a and carotenoids of the rhodo-pinal group.

Strictly anaerobic and obligately phototrophic. Sulfide-reduced media required. Sulfide and S0 used as photosyn-thetic electron donors. In the presence of sulfide and bicarbonate, acetate and pyruvate are photoassimilated. Not utilized: thiosulfate, sugars, alcohols, higher fatty acids, amino acids, benzoate, formate, and most intermediates of the tricarboxylic acid cycle. Assimilatory sulfate reduction is absent. Nitrogen sources: ammonium salts, urea, and N2. Vitamin B12 required.

Freshwater bacterium with optimum growth at 25-30°C and pH 7.0 (pH range 6.5-7.3).

Habitat: ditches, ponds, and lakes with stagnant freshwater containing hydrogen sulfide and exposed to light.

The mol%o G + C of the DNA is: 55.1-60.2 (Bd); type strain 55.1 (Bd).

Type strain: 6512, ATCC 14959, BN 5810, DSM 173.

GenBank accession number (16S rRNA): Y12365.

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